This invention relates to clamping or gripping devices for wire rope and particularly to an improved wedge socket for clamping the end of a cable.
Wedge sockets are among the simplest devices for anchoring a wire rope or cable for any of numerous purposes. They are intended for "on the job" attachment and for quick rope replacement. Principal advantages are simplicity, ease and speed of applying and detaching. They are also used where conditions are such that spliced eyes cannot be reeved and would have to be made after the rope is in place. Wire lines, commonly called cable, are used with lifting machines such as cranes. The wire hangs over a pulley from the crane and has a free end dangling down below. Wedge sockets are typically connected to this lower end of the wire rope and a hook or other member is attached to the socket. Thus, the socket provides means for coupling the free end of the wire rope to buckets or other apparatus which are then lifted or transported by a crane.
Typical open wedge sockets include a wedge member and a socket for receiving the wedge member. A cable is captured in the socket by passing the free end of the cable through the socket, laying the wedge on the cable, and returning the free end of the cable over the wedge and back through the socket. As the size of the wire rope increases, the difficulty of this manual manipulation increases. To achieve the turnback, much more wire rope is used than is necessary for the final assembly. After assembly, the excess is trimmed off and discarded.
Some device is usually attached to the dead end segment of the wire rope to facilitate the moving of the wedge into the socket when the initial load is applied. Also this device prevents slippage if slack is induced into the system by something striking the stub end of the wire rope or the small end of the wedge. Another problem is that the wire rope can be installed in reverse position which will cause a relatively sharp kink in the wire rope when the wire rope is applied.
There has been similar effort to overcome some of the concerns listed above by using a wedge as socket inside a concave shaped basket. Typical of this type socket is that represented by U.S. Pat. No. 3,351,986. This type socket overcomes some of the concerns with the more commonly used wedge socket. However, those designs have some shortcomings, such as: 1. They require a high degree of initial clamping effort to insure that the wire rope will not slip through the rope channel during initial load application. Most of the present clamps of this general configuration contains a U-bolt. This clamping effort comes from such U-bolt which after initial load application must be retightened. This concentrated clamping force on the live end of the wire rope has a reducing effect on the potential fatigue life of the termination. Also, it has a reducing effect on the termination efficiency. The U-bolt clamps wedge elements outside of the basket and is unsightly and can snag objects with which it might come in contact. Further the wedge surface that contacts interior surface of the socket is convex allowing for concentrated load transmission to the socket.
It is thus seen that there is a need for a wedge socket which overcomes the shortcomings.
As additional background, it should be stated that the efficiency of a termination (end of wire rope secured in socket) is a rating derived as a ratio of the rated catalog working strength of the wire rope to the breaking strength of the wire rope when used in a termination. As an explanation of the significance of this rating the following example is offered in which a certain size and class of wire rope has a rated catalog ultimate strength of fifty thousand pounds. If this wire rope were used with the wedge socket having an efficiency of termination of eighty percent then the expected resulting ultimate strength of the wire rope would be forty thousand pounds. The reduction in the relative strength of the wire rope is caused by the severe compression of the wire rope in the region where the wire rope/wedge/basket interface.
A system designer must use the termination rating to derive the proper rated capacity of the wire rope. For example, under OSHA regulations, the running lines on a mobile crane must have a safety factor of at least 3.5. Using a crane that has an adequate line pull and stability and using a fifty thousand pound wire rope with an eighty percent wedge socket for a single part line, the maximum allowable load to be lifted would be 50,000.times.0.8 divided by 3.5=11,428 pounds. If however,the wedge socket has a ninty five percent efficiency rating, the maximum allowable load would be 50,000.times.0.95 divided by 3.5=13,571 pounds. The importance of a high termination rating is thus quite apparent.